Electric oven

ABSTRACT

An electric oven for rapidly heating therein frozen convenience food in containers placed on plates having a thermal conductivity approximately equivalent to that of the food and means for pulsing heat energy upwardly through the plate and container into the food mass at timed intervals, pulsing infrared heat downwardly into the food mass at a predetermined wavelength range while reflecting a portion of the infrared heat to produce a required ambient condition, and regulating the air temperature within the oven, whereby a maximum tolerable rate of temperature rise in the food by conduction, radiation, and convection is provided.

United States Patent [72] Inventor Stanley vJoeckel 3,155,814 11/1964Appleman et a1 219/407 Wayne, NJ. 3,176,118 3/1965 Scott 219/394 [21]Appl. No. 93,762 3,244,859 4/1966 Whiteford 219/405 X [22] Filed Nov.30, 1970 3,249,741 5/1966 Mills 219/41 1 [45] Patented Dec. 7,19713,261,394 7/1966 Foster et al.. 165/12 [73] Assignee lrex Corporation3,265,861 8/1966 Perlman 219/41 1 X R1verdale,N.J. 3,313,917 4/1967Ditzler et a1. 219/400 3,460,460 8/1969 Bixby et a1. 99/327 5 PrimaryExaminer-Volodymyr Y. Mayewsky 4 claims 6 Drum": Fig, Auorney- Leo C.Krazinski [52] U.S. Cl 219/411,

99/327, 165/12, 219/398, 219/407, 219/413, ABSTRACT: An electric ovenfor rapidly heating therein 219/490 frozen convenience food incontainers placed on plates having [51 Int. Cl F27d 11/02 a thermalconductivity approximately equivalent to that of the [50] Field ofSearch 219/400, food and means for pulsing heat energy upwardly throughthe 398, 405,406, 407,409,410,411,412,413,480, plate and container intothe food mass at timed intervals, 1 492, 490; 99/327; 165/12 pulsinginfrared heat downwardly into the food mass at a predeterminedwavelength range while reflecting a portion of References Cited theinfrared heat to produce a required ambient condition, UNITED STATESPATENTS and regulating the air temperature within the oven, whereby a2,860,225 11/1958 Steen 219/411x maximum. tolerable rate of temperaturerise in the food by 3 032 35 5 19 2 Schauer, jl-m' 2|9/413 x conduction,radiation, and convection is provided. 3,059,087 10/1962 Perlman 219/411X "a F K]:

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PATENTEB DEC 7 am 'SHEET 1 [IF 4 V INVENTOFZ EH STANLEH' V. JOEZCKEL.

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saw u or 4 PILOT LRMP TOP HEATING \NVENTOR' QTTORNEY BOTTOM HERHNGELEMENT? ELEMENTB By STANLEY JOECKEL auzzea CONTROL TOP HEAT CONTROLSWITCHl BOTTOM HEHT CONTROL.

ELECTRIC ovEN BACKGROUND or THE INVENTION Field of Invention The presentinvention relates to electric ovens and, more particularly, to electricovens adapted for quickly heating frozen convenience foods, packed inflat, thin pans, to customer'serving temperatures.

Heretofore, conventional ovens for heating frozen food have employedinfrared radiation directed from both above and below the food, as inStien US. Pat. No. 2,860,225; by a rotatable grill exposed to infraredradiation, as in Bixby et al., US. Pat. No. 3,460,460; and by pulsatingheat through the food, as in Foster et al., US. Pat. No. 3,261,394. Suchovens, however, are not suitable for quickly heating frozen conveniencefoods efficiently for use particularly in large establishments, such ashospitals, colleges, nursing homes, large restaurants and the like.

It was discovered after experimentation that the limiting.

factor in heating frozen food products was the thermal conductivity ofthe food itself. Consequently, the method of applying heat energy to thefood (whether infrared, convection, and or conduction) is a secondaryconsideration. After further experimentation it was discovered that noone method of applying heat energy could produce the desired effect ofquickly heating a frozen convenience food product from to 170 F.

Efforts were then directed to determine how to produce the maximumenergy input to the food to accomplish optimal heating thereof withoutthe necessity of (a) applying special coatings to the containers, (b)stirring the food within the container during the heating cycle, (c)prior thawing the food, and (d) destroying the original quality of thefood, that is, without scorching excessive dehydration, flavor change,loss of nutrients, etc. i

It was also discovered that the material on which the food pan wasplaced had to have a thermal conductivity compatible with the frozenfood placed thereupon. (Since most foods contain a very high percentageof water, the thermal conductivity of foods was considered to beconstant.) The conductive plate material chosen was Hercuvit 106 by PPGIndustries, a

glass ceramic material, having a thermal conductivity of about 0.004Cal./cm. /sec./C. The thermal conductivity of water containing salt infood is approximately 0.00l60.0020. This is to be compared with aluminum(a common material used in cooking), which has a thermal conductivity of0.5 or approximately I25 times as great as Hercuvit.

It was also discovered that the thickness of the plate (onefourth inch),the wattage of the energy source (approx. 600 w./sq. ft.) under theplate, the temperature which the side of the plate adjacent to thesource was allowed to reach (450 F.) and the energy input time cycle(approx. 30 percent to 70 percent of 5 minutes) were very important.Controls were therefore employed to pulse the input energy so as topermit the maximum tolerable energy flow, by conduction, from the heatsource through the plate, throughthe food container and into the frozenfoods mass. The result was to create the maximum tolerable rate oftemperature rise in the food which the con- 7 ductive principle wouldprovide.

In addition, a top radiation source, controlled by an infinitetypecontroller, was designed to provide the proper frequency range (approx.3 to l0 microns) to allow a portion of the heat to be absorbed by thefood in the pan while the remainder was used to produce the requiredambient condition. An ambient control was also provided to prevent theoven air temperature (approx. 800 F. max.) from exceeding those limitswhich would destroy the original quality of the food.

As above indicated, this invention therefore utilizes three heatingprinciples, conduction, radiation and convection combined in an uniquecontrolled way to achieve an optimal desired effect in rapidly bringingfoods from a frozen or otherwise refrigerated state to servingtemperatures in a manner which no single heating principle cansatisfactorily accomplish.

SUMMARY OF THE INVENTION Accordingly, an object of the invention is toprovide a new and improved heating arrangement particularly for frozenconvenience foods.

Another object of the invention is to provide such an electric oven thatutilizes in an efficient manner the combination of conduction, radiationand convection in quickly heating frozen convenience foods.

Still another object of the invention is to provide an improved electricoven in which frozen convenience foods are heated to required servingtemperatures for consumption within a much shorter time period than ispossible with conventional ovens.

Other and further objects will be obvious upon an understanding of theillustrative embodiment about to be described, or will be indicated inthe appended claims and various advantages not referred to herein willoccur to one skilled in the art upon employment of the invention inpractice;

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of theinvention has been chosen for purposes of illustration and descriptionand is shown in the accompanying drawings, forming a part of thespecification, wherein:

FIG. I is a front elevational view of an electric oven in accordancewith the present invention.

FIG. 2 is an end elevational view of the electric oven, as viewed fromthe right side of FIG. 1 in the direction of the arrow 2, showing theoven door closed in full lines and the oven door open in dotted lines.

FIG 3 is a horizontal sectional view of the electric oven taken alongline 3-3 of FIG. I with parts broken away to reveal interiorconstruction and the cover shown in elevation.

FIG. 5 is a perspective view of a plurality of electric ovens stackedone upon another.

FIG. 6 is a diagram of the circuitry for controlling the electric oven.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. l-4 ofthe drawings in detail, there is shown an electric oven of the inventioncomprising a casing 11, preferably of stainless steel construction,having, as viewed in FIG. 1, a top 12, a bottom 13, a right side 14, aleft side 16, and, as viewed in FIG. 2, a back 17 and a front 18 with abottom-hinged door 19, the bottom 13 being supported upon legs 21. Asmore readily evident in FIG. 4, the front 18 and back 17 of the casing11 and portions of the bottom 13 and top 12 thereof, as well as the door19, are provided with insulation 22. A top cover 23 for the casing isalso provided with the insulation 22. In both the top 12 and bottom 13are included infrared heating elements 24 and 25, respectively, backedby insulation 26, so that the infrared energy is directed inwardlywithin the oven-cooking compartment 27. Preferably, the infrared-heatingelements 24, 25 and insulation 26 used in the oven of this invention aredisclosed in pending application, Ser. No. 870,867, filed July 24, 1969,and which matured into US. Pat. No. 3,564,207 issued on Feb. 16, l97l.

Above the bottom-heating element 25, as viewed in FIG. 4, is shown aconductive plate 28, preferably Hercuvit 106 of PPG Industries, a glassceramic material, having a thermal conductivity of 0.004 Cal./cm. /sec./C. Since there is a high percentage of water in food, including somesalt, it can be assumed that the thermal conductivity of food issubstantially equal to that of water, which is about 0.00 l 6-0.0020. Asaluminum is a material that is commonly used as a container inconvenience foods, its thermal conductivity of 0.5 is about I25 times asgreat as that of Hercuvit." With a thickness of one-fourth inch for theHercuvit" plate 28 an energy source of about 600 w./sq. ft. under theplate 28 is impressed to provide a temperature of about 450 F. at thatunderside and kept for various time intervals, that is, the energy inputcan be pulsed so as to be ON 30 percent and OFF 70 percent of 5 minutes,or ON 40 percent, OFF 60 percent, ON 70 percent, OFF 30 percent, etc.This permits the maximum tolerable energy flow, by conduction, throughthe plate 28, through the aluminum food container 29 and into the foodmass 31.

Referring still to FIG. 4, the top infrared-heating element 24 deliversheat energy at a wavelength ranging from about 3 to microns allowingabout 30 percent of the heat energy to be absorbed by the container 29and top 32, while the remaining heat energy is reflected to produce therequired ambient condition, as will appear hereinafter. If the cover 32is removed from the container 29, a larger portion of the heat energy isdirectly absorbed by the food, while a smaller amount of the energyproduces the ambient condition. Of course, to accomplish the properheating efficiency in the compartment 27 the door 19 must be closed; butthe door must also be thoroughly insulated. The door 19 is coupled tothe casing 11 at its bottorn by a hinge 33, has ahandle 34 at its frontfor manipulation thereof, an insulated rear extension 36 that projectsinto the compartment 27, and to further seal the compartment in itsclosed position a gasket 37 is included at its rear peripheral faceadjacent the extension 36.

Referring again to FIG. 1, the oven 10 includes at its right portion anelectrical compartment 38 for housing electrical components and having apanel 39 for mounting the same with a louvered access panel 41 (FIG. 2)at its right side 14. Adjacent the top of panel 39 is shown a knob 42for a 60 minute interval timer, below which are control knobs 43 and 44for the bottom-heating element 25 and top-heating element 24,respectively, and adjacent the bottom a knob 46 for an oven temperaturecontrol. An oven temperature pilot lamp 47 is shown adjacent the knob46. A power disconnect switch 48 is provided on the right side 14,adjacent panel 41 for turning on and off the power supply to the oven10.

Referring now to FIG. 6, wherein the electrical supply and controlsystems are represented schematically, the main power supply is from apair of alternating current supply leads 49 and 51 of suitable voltage,such as 208 or 230 volts, alternating current. Since the invention willbe more clearly understood by tracing the operations involved, let it beassumed that it is desirous to heat frozen convenience food packed inflat, thin pans or containers ranging up to l2inches 20 inchesXZ'Ainches in size and being of aluminum material for both the pan andcover. Two of these food containers 29 are placed in the compartment 27of the oven 10, after a warm-up of the oven, the door 19 closed and thecircuit breaker 52, which was initially actuated to bring the powersupply via leads 53 and 54 to the oven temperature control unit 56, lead53 connecting to terminal 57 thereof and lead 54 connecting to lowerterminal 2 of terminal block 58, jumpered to lower terminal 3 of block58 and thence'via lead 59 through oven temperature control pilot lamp47, lead 62 to lower terminal 1 of block 58 and via lead 63 to terminal64 of the oven temperature control unit'56. The oven temperature controlunit 56 controls flow of current to all electrical components except themechanical timer unit 66, which is energized by lead 67 running fromterminal, 57 to terminal 68 and through the timer 66, and thence byparallel paths in which lead 69 connects through timer pilot lamp 72 andlead 73 to upper terminal 2 of block 58 and in which lead 74 connectsthrough buzzer 76 and lead 77 also to upper terminal 2 of block 58.

When the oven temperature control unit 56 is in the OFF position, nocurrent flows except to the timer unit 66, as indicated hereinbefore. Ifthe timer unit 66 is set to a predetermined time interval, the timerpilot lamp 72 and buzzer 76 will operate at the end of the timeinterval, independent of any tom heat control unit 79 may be traced fromthe circuit breaker 52 over lead 53 to terminal 57 of and through theoven temperature control unit 56, terminal 64 thereof, over lead 81,through resistor 82, over lead 83, through bottom heat control unit 79and thence over lead 84 to terminals 2 of block 58 and back over lead 54to the circuit breaker 52, whereupon the bottom heat control unit 79 isenergized to close a switch 86 for energizing the bottom-heatingelements 25 over a circuit from terminal 64 of oven temperature controlunit 56 via lead 63, terminals 1 of block 56, lead 87, through actuatedswitch 86 via lead 88, terminals 4 of block 58, leads 89 throughbottom-heating elements 25, and thence via leads 91 through terminals 3and 2 of block 58 and via lead 54 to the circuit breaker 52. Similarlythe circuit for the top heat control unit may be traced from the circuitbreaker 52 over lead 53 to terminal 57 of and through the oventemperature control unit 56, terminal 64 thereof, over lead 63,terminals l of block 58, lead 92, through top heat control 78, over lead93 to terminals 2 of block 58, and back over lead 54 to the other sideof circuit breaker 52, whereupon the top heat control unit 78 isenergized to close a circuit for the top-heating elements 24 that can betraced therefrom via lead 94 through terminals 6 block 58, via leads 96through top-heating elements 24 and thence back over leads 97, throughterminals 5 of block 58 and over lead 98 to the other side of top heatcontrol unit 78.

The top heat control unit 78 is an adjustable short interval pulsingdevice for regulating flow of current to the top radiant heatingelements 24; while the bottom heat control unit 79 is an adjustable longinterval pulsing device for regulating flow of current to the bottomradiant heating elements 25. As traced hereinbefore, both the top heatcontrol unit 78 and the bottom heat control unit 79 are supplied withcurrent from the oven temperature control unit. The pilot lamp 47indicates when current is flowing through oven temperature control unit56 and its circuit may be traced from one side of circuit breaker 52 vialead 53, terminal 57, through oven temperature control unit 56, terminal64, over lead 63 to terminal 1 of block 58, thence over lead 62 throughpilot lamp 47, over lead 59 to terminals 3 and 2 of block 58 and backover lead 54 to the other side of the circuit breaker 52.

Briefly, in heating frozen convenience food the oven is first preheatedafter which the frozen food which is disposed in aluminum pans 29covered by aluminum foil 32 is placed in the compartment 27 (FIG. 4) onthe Hercuvit" conduction plate 28 and the door 19 is closed. The'oventemperature control unit 56, which is calibrated in degrees Fahrenheit,is then set by turning knob 46 (FIG. 1) to the desired degree setting inorder to regulate the optimal temperature within the compartmeat 27. Thepilot lamp 47 will be extinguished when the set temperature is reached.This temperature is programmed to allow the highest energy output thatthe particular food product can absorb without burning the food. It hasbeen found that there is a direct relationship between the interval ofthe applied electrical energy (pulsed heat) and the ability of the foodproduct to absorb this energy rapidly without burning. The top-heatingelement 24 radiates directly on the aluminum foil cover 32 of the foodpan 29 or directly upon the food, if the cover is removed. This heatsource is capable of being pulsed when the type of food being warmedrequires it by turning knob 43 from L0 to HI, the low setting giving thesmallest amount of radiant heat. The bottom-heating element 25 isregulated by the bottom heat control unit 79 to pulsate heat to theHercuvit plate. A setting of l or lower of the knob 44 gives theshortest heat pulsation while a setting of 9 or higher produces thelongest heat pulsation. Both the top and bottom heaters act to raise theambient temperature in the oven compartment 27, so that the food is alsobeing warmed by convection. The food, therefore, is subjected to acontrolled heating cycle, which pumps heat into the product on allsurfaces, through the bottom by conduction, through the top by radiationand all around four sides by convection. The timer unit 66 has a maximumtime setting of 60 minutes. In

order to set the timer unit the knob 42 is rotated clockwise (FIG. 1) tothe desired time interval and, when the set time interval has elapsed,the buzzer 76 will be actuated as an audible sound and the timer pilotlamp 72 will be lighted to indicate that the food should be removed fromthe oven. Since the timer unit 66 does not automatically turn to OFFposition, both the lamp 72 and buzzer 76 are deactivated by rotating theknob 42 counterclockwise to its OFF position.

[t has been found that a wide variety of casserole type of frozen foodstake about 60 minutes to reconstitute in conventional-type ovens, whileovens of this invention accomplish the same object in from to minutes.

In FIG. 5 is shown a plurality of electric ovens l0 stacked one uponanother. This offers the advantage of being able to reconstitutedifferent types of frozen food at the same time, since each oven isindividually controlled and not affected adversely by the oven above orbelow it.

From the foregoing description it will be seen that the presentinvention provides an electric oven that can quickly reconstitute frozenconvenience foods by utilizing in a novel manner conduction, radiationand convection.

As various changes may be made in the form, construction, andarrangement of the parts herein, without departing from the spirit andscope of the invention and without sacrificing any of its advantages, itis to be understood that all matters are to be interpreted asillustrative and not in any limiting sense.

What is claimed is:

1. An electric oven comprising a compartment for heating frozenconvenience food packaged in an aluminum pan, said compartment having atop wall, a bottom wall, two sidewalls, a backwall and an open front endin which each of said walls is backed with insulation, a plate disposedon said bottom wall for supporting said packaged food, said plate havinga thermal conductivity of about 0.004 CaL/cmF/secj" C., approximatelyequivalent to that of the food, and having a thickness of aboutone-fourth inch, a door for closing the open front end of saidcompartment, said door being hollow and provided with insulation, anelectric heating element at said top wall of said compartment fordirecting infrared rays downwardly upon said packaged food. said topheating element being adapted to deliver heat energy in a wave lengthranging from about 3 to 10 microns in order to allow some of the heat tobe absorbed by the food in the pan while the remainder of the heatproduces a required ambient condition within the compartment, electriccontrol means for pulsing input wattage to said top heating element, anelectric heating element at said bottom wall of said compartment forconducting heat upwardly through said plate into said packaged food,said bottom heating element being adapted to deliver a wattage of about600 w./sq. ft. to said conductive plate, which latter is allowed toreach a maximum of about 450 F., electric control means for pulsinginput wattage to said bottom heating element at an input cycle of about30 to percent of 5 minutes, so as to permit maximum tolerable energyflow by conduction through said plate, food pan and into the frozenfood, and electric control means for regulating the temperature withinsaid compartment so as to prevent the ambient condition from exceedingan oven air temperature of about 800 F., all of said electric controlmeans being manually operable and said electric control means for saidtop and bottom heating elements being responsive to said temperaturecontrol means.

2. An electric oven in accordance with claim 1, and a manually operabletiming means for setting a desired time interval for operation of theheating elements.

3. An electric oven in accordance with claim 2, and a pilot lamp andbuzzer operable after said time interval has elapsed.

4. An electric oven in accordance with claim 1, in which said door ispivotally attached to said oven.

1. An electric oven comprising a compartment for heating frozenconvenience food packaged in an aluminum pan, said compartment having atop wall, a bottom wall, two sidewalls, a backwall and an open front endin which each of said walls is backed with insulation, a plate disposedon said bottom wall for supporting said packaged food, said plate havinga thermal conductivity of about 0.004 Cal./cm.2/sec./* C., approximatelyequivalent to that of the food, and having a thickness of aboutone-fourth inch, a door for closing the open front end of saidcompartment, said door being hollow and provided with insulation, anelectric heating element at said top wall of said compartment fordirecting infrared rays downwardly upon said packaged food, said topheating element being adapted to deliver heat energy in a wave lengthranging from about 3 to 10 microns in order to allow some of the heat tobe absorbed by the food in the pan while the remainder of the heatproduces a required ambient condition within the compartment, electriccontrol means for pulsing input wattage to said top heating element, anelectric heating element at said bottom wall of said compartment forconducting heat upwardly through said plate into said packaged food,said bottom heating element being adapted to deliver a wattage of about600 w./sq. ft. to said conductive plate, which latter is allowed toreach a maximum of about 450* F., electric control means for pulsinginput wattage to said bottom heating element at an input cycle of about30 to 70 percent of 5 minutes, so as to permit maximum tolerable energyflow by conduction through said plate, food pan and into the frozenfood, and electric control means for regulating the temperature withinsaid compartment so as to prevent the ambient condition from exceedingan oven air temperature of about 800* F., all of said electric controlmeans being manually operable and said electric control means for saidtop and bottom heating elements being responsive to said temperaturecontrol means.
 2. An electric oven in accordance with claim 1, and amanually operable timing means for setting a desired time interval foroperation of the heating elements.
 3. An electric oven in accordancewith claim 2, and a pilot lamp and buzzer operable after said timeinterval has elapsed.
 4. An electric oven in accordance with claim 1, inwhich said door is pivotally attached to said oven.